Find the missing value. $2=18\div{?}$ $?=$
Solution: We can think of division as the following: ${\text{size of the groups}}=C{\text{total}} \div {\text{number of groups}}$ We have $C{18}$ total. When we have ${2}$ in each group, what is the ${\text{number of groups}}$ ? $ {2} = C{18} \div {?} $ $18$ $2$ $? \text{ equal groups}$ ${9} \times {2} = C{18}$ There are ${9}$ groups. $18$ $2$ $2$ $2$ $2$ $2$ $2$ $2$ $2$ $2$ $9 \text{ equal groups}$ $ {2} = C{18} \div {9} $ ${?}={9}$